[PATCH] [gdb/cli] Document \001 and \002 usage for set prompt

[PATCH] [gdb/cli] Document \001 and \002 usage for set prompt

[Tom de Vries]

PR cli/28887 reports the following problem when using a custom prompt.

First, we set up the custom prompt (with ^ marking the position of the
blinking cursor on the line above):
...
$ gdb -q -ex "set prompt \033[31mgdb$ \033[0m"
gdb$
     ^
...

Then we type some string, and enter it into the command history:
...
gdb$ some long command
❌️ Undefined command: "some".  Try "help".
gdb$
     ^
...

We use C-p to fetch the previous command:
...
gdb$ some long command
                      ^
...
Sofar, so good.

Finally, we use C-a which should move the cursor to just after the prompt, but
instead we get:
...
gdb$ some long command
              ^
...

This is fixed by using \001 and \002:
...
(gdb) set prompt \001\033[31m\002gdb$ \001\033[0m\002
...
aka as RL_PROMPT_START_IGNORE and RL_PROMPT_END_IGNORE [1].

Add an example to the documentation showing the use of these markers.

The added example is the equivalent of the "\[\e[0;34m\](gdb)\[\e[0m\]"
example documented at gdb.prompt.substitute_string that can be used with
"set extended-prompt".

While working on this, I noticed that "show prompt" doesn't show back the
original string, using '\e' instead of '\033':
...
gdb$ show prompt
Gdb's prompt is "\001\e[31m\002gdb$ \001\e[0m\002".
...
and that the shown string can't be used as an argument to "set prompt":
...
gdb$ set prompt \001\e[31m\002gdb$ \001\e[0m\002
e[31mgdb$ e[0m
...

I've filed this as PR cli/33184.

[1] https://tiswww.case.edu/php/chet/readline/readline.html
---
 gdb/doc/gdb.texinfo | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 35b770f8138..0a2d34756eb 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -27659,6 +27659,16 @@ or a prompt that does not.
 @item set prompt @var{newprompt}
 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
 
+For example, this will set a blue-colored ``(gdb)'' prompt:
+
+@smallexample
+set prompt \001\033[0;34m\002(gdb)\001\033[0m\002
+@end smallexample
+
+It uses ``\001'' and ``\002'' to begin and end a sequence of
+non-printing characters, to make sure they're not counted in the string
+length.
+
 @kindex show prompt
 @item show prompt
 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}

base-commit: cfbf9925c1c34f9e9d47c8b29d165866557663e3
-- 
2.43.0

Re: [PATCH] [gdb/cli] Document \001 and \002 usage for set prompt

[Eli Zaretskii]

> From: Tom de Vries <tdevries@suse.de>
> Date: Sat, 19 Jul 2025 08:16:36 +0200
> 
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 35b770f8138..0a2d34756eb 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -27659,6 +27659,16 @@ or a prompt that does not.
>  @item set prompt @var{newprompt}
>  Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
>  
> +For example, this will set a blue-colored ``(gdb)'' prompt:
> +
> +@smallexample
> +set prompt \001\033[0;34m\002(gdb)\001\033[0m\002
> +@end smallexample
> +
> +It uses ``\001'' and ``\002'' to begin and end a sequence of
> +non-printing characters, to make sure they're not counted in the string
> +length.

Please use @samp to quote \001 etc., not literal quotes.

OK with that nit fixed.

P.S. Does this work on MS-Windows console as well?

Approved-By: Eli Zaretskii <eliz@gnu.org>

Re: [PATCH] [gdb/cli] Document \001 and \002 usage for set prompt

[Tom de Vries]

On 7/19/25 08:47, Eli Zaretskii wrote:
>> From: Tom de Vries <tdevries@suse.de>
>> Date: Sat, 19 Jul 2025 08:16:36 +0200
>>
>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>> index 35b770f8138..0a2d34756eb 100644
>> --- a/gdb/doc/gdb.texinfo
>> +++ b/gdb/doc/gdb.texinfo
>> @@ -27659,6 +27659,16 @@ or a prompt that does not.
>>   @item set prompt @var{newprompt}
>>   Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
>>   
>> +For example, this will set a blue-colored ``(gdb)'' prompt:
>> +
>> +@smallexample
>> +set prompt \001\033[0;34m\002(gdb)\001\033[0m\002
>> +@end smallexample
>> +
>> +It uses ``\001'' and ``\002'' to begin and end a sequence of
>> +non-printing characters, to make sure they're not counted in the string
>> +length.
> 
> Please use @samp to quote \001 etc., not literal quotes.
> 
> OK with that nit fixed.
> 

Hi Eli,

thanks for the review, pushed with that nit fixed.

> P.S. Does this work on MS-Windows console as well?
> 

A good question.

I suppose the \001\002 part should work, because it's handled by 
readline (assuming readline is always used).

The \033 bits, probably not.  I read this wikipedia article ( 
https://en.wikipedia.org/wiki/ANSI_escape_code ) which has some info on 
that, so a current powershell should work AFAIU.

I tried to test this on my windows laptop, but I didn't manage to run 
gdb on it in either windows console or powershell, though the cygwin 
shell did work.

Thanks,
- Tom

> Approved-By: Eli Zaretskii <eliz@gnu.org>